Take two bowls. In one, add the sugar, flour, baking powder, baking soda, salt, lemon zest and poppy seeds. Mix with a whisk.
In the second bowl, add the eggs, milk, lemon juice and sunflower oil. Mix together with a whisk.
Pour the milk mixture directly into the dry ingredients and use the whisk and/or spatula to mix until smooth. It doesn't matter if there are small lumps here and there.
Place the paper muffin tins in a cupcake pan and fill with the batter. Fill the muffins just below the rim so that there will be a nice ball on top when they rise in the oven.
Bake for 18-20 minutes at 200°C/400℉ (conventional oven) or until golden brown.
How to store
Keep in an airtight container outside the refrigerator for about 5 days. They can also be frozen and will keep for up to 3 months.